Apparatus for establishing and maintaining an atmosphere controlled as to pressure, temperature, gas content and rate of gas flow, and closed and semi-closed arc heater loop apparatus for use therein



2 1968 G. A. KEMENY ETAL 3,371,189

APPARATUS FOR ESTABLISHING AND MAINTAINING AN ATMOSPHERE CONTROLLED ASTO PRESSURE, TEMPERATURE, GAS CONTENT AND RATE OF GAS FLOW, AND CLOSEDAND SEMI-CLOSED ARC HEATER LOOP APPARATUS FOR USE THEREIN Filed Aug. 20.1964 4| A POWER 2 43 SUPPLY 4 7 FlG.l.

ARC 23 HEATER TEMPERATURE 28 SENSING 30 3| p 18 GAS DEVICE v SOURCE ll38 34 |9 24 l4 l5 F|G'3 SOURCE -26 3s v J V? 42 DUST F IG-Z- s SE A T R53 P 0 ARC? POWER 43 37 J PRE-COOLER 5| 33 HEATER SUPPLY TEMPERATURE Lyl8 26 SENSING DEVICE 6|. 6 34 29/ GAS T SOURCE u 38 V 2 1 v 31 30 mmPRE-COOLER 34 -|3 52%] I7 2% Elm DUST I I5 SEPARATOR V 66 WITNESSESGeorg f Kl rsgn y MJW 8. Peter E Kienosf United States Patent APPARATUSFOR ESTABLISHING AND MAIN- TAINING AN ATMOSPHERE CONTROLLED AS TOPRESSURE, TEMPERATURE, GAS (IONTENT AND RATE OF GAS FLOW, AND CLOSED ANDSEMI-CLOSED ARC HEATER LOOP APPARATUS FOR USE THEREIN George A. Kemeny,Franklin Township, and Peter F. Kienast, Pittsburgh, Pa., assignors toWestinghouse Electric Corporation, Pittsburgh, Pa, a corporation ofPennsylvania Filed Aug. 20, 1964, Ser. No. 390,898 8 Claims. (Cl.219-383) ABSTRACT OF THE DISQLOSURE Loop apparatus for providing acontrolled atmosphere controlled as to pressure, temperature, gascontent and rate of gas flow, especially suitable for metal working ingases at high temperatures, includes an arc heater having an energizingcircuit and having compressed gas at a predetermined pressure and rateof flow supplied thereto to be heated to a desired temperature, and afurnace operatively connected to the arc heater for utilizing the gasfor metal working, and including means forming a closed loop forrecycling gas through the furnace. Additionally, means is provided forremoving a predetermined minor portion of gas from the closed loop at apredetermined pressure and rate of flow to maintain the pressure andrate of gas flow in the furnace substantially constant. Some embodimentsemploy a preheater, heated by the removed gas, to preheat gas suppliedto the'arc heater; others employ in addition to a preheater a dustseparator circuit for cleaning removed gas, and after it is used in thepreheater, feeding it back into the arc heater to thereby reduce thetotal quantity of gas required for operation of the furnace.

This invention relates to improvements in methods and apparatus forproviding controlled atmospheres in closed and semi-closed loop systems,especially suitable for metal working in gases at high temperatures, andparticularly to such loops using arc heaters for heating the gases.

As will be readily understood by those skilled in the art, in metalworking it is necessary to raise metals to tempering, annealing, meltingor reducing temperatures, and in some processes it is further necessaryor desirable to control the specific atmosphere in which the metal isheated.

Apparatus suitable for practicing the methods of our invention employsan arc heater which passesthe gas to be heated through an are whichrotates between water cooled electrodes. The high speed of rotation ofthe arc provides uniform enthalpy and temperature at the gas injector.The are heater transforms electric energy to heat energy directlywithout the need for conventional heating elements or consumableelectrodes. This makes it possible to achieve very. high gas temperatureWithout contamination. Since the arc heater is especially suited forhigh temperature operation, only a small quantity of gas flow isrequired to raise the operating temperature in the furnace to therequired value thereby increasing the efiiciency of the method andapparatus.

The apparatus is also especially suitable for use in systems or anyapplication requiring high temperature gas flows, and is characterizedby high efficiency of operation, continuous operation, temperaturecontrol in the furnace, pressure control in the furnace and throughoutthe systern, the ability to produce temperatures required for a widerange of particular applications, and control of the specific atmospherein the system.

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To this end, the apparatus embodying our invention and suitable forpracticing the method of our invention includes an arc heater the gasinput to which is or may be supplied through a heat exchanger. Theheated gas from the arc heater is supplied to means forming a closedpath, the path forming means including a furnace portion of enlargeddiameter for containing the metal or other substance to be heated,having a door for placing the metal inside the furnace. A tempearturesensing device connected inside the furnace near the substance to beheated is connected to a control which automatically regulates the powerinto the arc heater and accordingly regulates the temperature of gas inthe arc heater. Gas from the arc heater, after passing around the closedpath and around the metal to be heated returns to a point in the closedchannel or closed path near the point of injection, from whence aportion of it passes through the heat exchanger and is exhausted. Thefraction of gas discharged from the main loop may be bled from any partof the main loop but for efficiency reasons it is desirable that thisgas be ejected from a location downstream of the furnace portion of theloop. A large portion of the gas is recycled.

In another embodiment of the inveniton, the portion of the gas removedfrom or allowed to escape from the closed path, after passing throughthe heat exchanger, is precooled and then passed through a dustseparator or other filter and supplied back into the arc heater. Thistype of configuration is particularly attractive if the heated gas issufliciently expensive to make it economically unattractive to waste aportion of the gas flow.

In both embodiments, an additional input or inputs are provided to themeans forming the closed path for supplying another gas or other gasesin addition to that heated by the arc heater, to provide an atmospherehaving any desired ratio of gas content. Heat is transferred from theheated gas to the unheated gas by convection.

An object of our invention is to provide a new and im proved method ofestablishing and maintaining an atmosphere controllable as to pressure,temperature, gas content, and rate of gas flow.

Another object is to provide new and improved apparatus for controllingan atmosphere, and offering advantages over any now existing in the art.

A further object of our invention is to provide new and improved closedand semi-closed loop apparatus employing an arc heater for heatingmetals in a controlled atmosphere.

An additional object is to provide a new and improved closed loop systemin which gas, after passing around the metal or other surfaces to beheated in the furnace, is filtered and channeled back through an archeater and thence recycled'through the heating furnace.

Another object of our invention is to provide a heat treating apparatuswherein an arc heater is used to heat all these gases presentlycontemplated for this application.

S ill a further object is to provide a new and improved heating furnacein which the atmosphere may be easily controlled.

These and other objects will become more clearly ap parent after a studyof the following specification, when read in conjunction with theaccompanying drawings, in which:

FIGURE 1 is a view partially in cross-section of semiclosed loop archeater apparatus according to our invention;

FIG. 2 is a view partially in cross-section of the preferred embodimentof a closed loop system embodying our invention; and

FIG. 3 is a view of a simplified embodiment of our in vention.

Referring now to the drawings, in which like reference numerals are usedthroughout to designate like parts, for a more detailed understanding ofthe invention, and in particular in FIG. 1 thereof, reference numeralgenerally designates a heating furnace having a portion 11 of enlargeddiameter with a door 12 therein; the substance to be treated, forexample a metal, is indicated at 13, mounted upon a suitable saucer orother support 14. In the illustrative drawing of FIG. 1, gas flows fromleft to right and exits from the furnace 10 into a conduit 15 which, asshown, loops back and is connected with the entrance end of the furnace,providing a closed loop or closed path for the flow of gases. There is achamber 16 of substantially enlarged diameter at the entrance end of theclosed furnace loop, having a throat of substantially reduced diameter17, having a gas inlet pipe 18 with a nozzle 1d closely adjacent thethroat 17. Gas entering the furnace area from the nozzle 19 is the gaswhich has been heated by the arc heater generally designated 23. Are

heater 23 has been shown externally located with respect to the loop.Actually the arc heater is relatively small and can also be located inchamber 16. The gas from nozzle 19 passes up a relatively long portion24 into the portion of enlarged diameter 11. It is seen that closelyadjacent the nozzle 17 on the furnace side thereof is an additional gasinlet pipe 25 connected to a gas source 26 shown in block form forconvenience of illustration. It will be understood that the inlet pipe25 may contain suitable valve means, and that the inlet itself mayconsist of separate holes or nozzles suitably directed, not shown forconvenience of illustration; gas entering from the pipe 25 entersobliquely or tangentially to gas entering 24 at the nozzle 19, whichassists in providing good mixing of the gases.

The aforementioned chamber 16 has a gas outlet conduit or pipe 28communicating with a heat exchanger generally designated 29. Gas fromconduit 28 after passing through the heat exchanger 2h is exhaustedthrough the outlet pipe 30 which contains a suitable valve 31. The valve31 is preferably a pressure-actuated valve for maintaining asubstantially constant pressure in the furnace generally designated 10.It is seen that in the heat exchanger 29, heat from the gas passingthrough conduit 28 is transferred to a pipe or conduit 33 which suppliesthe input to the arc heater 23, conduit 33 being connected to receivethe output of the compressor 34 connected to inlet pipe 35. Inlet pipe35 may be used if air is to be drawn into the system or if a desired gashas to be pressurized by means of compressor 34. Alternately, ifcompressed gas available in cylinders or from other sources is to beheated in the arc heater, compressor 34 may be eliminated.

It is seen that the furnace generally designated 10 has a temperaturesensing device 37 with a temperature responsive element 38 disposed inthe furnace 10. The temperature sensing device 37 supplies an output byWay of leads 41 and 42 to the power supply 43 which controls the powerinput to the arc heater. The temperature sensing device 37 accordinglyis connected to automatically control the power input to the arc heater23 to thereby maintain a constant predetermined gas temperature in thefurnace 10. It will be readily understood that, in accordance with therate of flow of gas or gases through the furnace, the temperaturesensing device may be readjusted or reset to maintaina predeterminedtemperature, and the temperature sensing device and power supply 43 areunderstood to include means, not shown for convenience of illustration,for varying the temperautre which is tobe maintained within the furnace10.

In the operation of the apparatus of FIG. 1, gas enteringinlet pipe 35,after compression at 34 and being preheatedby passing through the heatexchanger 29 is further heated in the arc heater 23. The operation ofgas are heaters is well known and need not be described herein indetail. For a fuller understanding of the manner in which electricalenergy is directly converted to heat energy in an arc heater, referencemay be had to Patent No. 3,048,736 entitled Arc Chamber by W. S.Emmerich, issued August 7, 1962 and assigned to the assignee of theinstant invention. The heated gas from are heater 23 passes through thenozzle 19 into the injection or aspirator system where it mixes with thecolder gas, which may include gas supplied from source 26, and inducesthe required flow velocity in the main heating loop including thefurnace having the chamber 11. Proportional mixing of the hightemperature gas from the arc heater and the other gas in the system willdetermine the furnace temperature. Material to be heated, illustratedgenerally at 13, is located in the furnace. The major portion of the gaswill recycle due to the aspiration effect and will again be mixed withand heated by the gas from nozzle 19, the arc heater output. A pressureactuated valve 31 regulates the system by enabling some, or a smallportion, of the gas to escape or be exhausted through a heat exchanger,thus preheating the gas being compressed into the arc heater. Due to thepresence of the heat exchanger, less electrical input will be requiredto raise the gas to the required temperature, thus increasing the systemefficiency. The temperature sensing device 37 including temperaturesensing element 38 controls the input power to the are heater 23 toachieve proper operating conditions. Preferably the furnace and ifdesired the entire recycling system has either brick lining, not shownfor convenience of illustration, or Water cooling, not shown forconvenience of illustration, depending upon the operating temperature,any convenient arrangement being suitable.

It is seen, then, that the apparatus of FIG. 1 provides an integratedsystem for heating metals for tempering, annealing, melting or reducing,and provides an integrated system for any process requiring heated gasflow. The apparatus and system of FIG. 1 provide complete control of theatmosphere of the heating process, and in the semi-closed loop system ofFIG. 1, the arc heater provides suificient action to maintain the gasflow. The need for blowers and compressors in the high temperature loopis thereby eliminated.

The apparatus of FIG. 1 is suitable for practicing the method of ourinvention, defined and claimed hereinafter, for establishing andmaintaining an atmosphere controlled as to pressure, temperature, gascomposition, and rate of gas flow.

Particular reference is made now to FIG. 2, which shows closed loopapparatus according to our invention. The apparatus of FIG. 2 differsfrom that of FIG. 1 in that outlet pipe 30', corresponding to outletpipe 30 of FIG. 1, supplies an input to a precooler 51, of anyconvenient design, which supplies an output by way of conduit 52 to adust separator or other filter 53, the output of the dust separator orfilter 53 being connected to the aforementioned input pipe, in this casepipe 35', supplying an input to the compressor 34.

In the apparatus of FIG. 2, gas discharge from the heat exchanger 29 isrecycled through the compressor. Otherwise the operation of theapparatus of FIG. 2 is similar to the aforedescribed operation of theapparatus of FIG. 1.

In the apparatus of FIG. 2, where gas is supplied from source 26 toprovide a mixture in furnace 10, a small portion of gas may be bled fromthe closed loop by bleeder 61 controlled by valve 62 to assist inmaintaining constant pressure in the closed path and furnace. The systemmay be initially charged with gas or gases through valve 66.

Pressure level in the furnace in either embodiment can be of any desiredlevel, including atmospheric pressure, which facilitates the chargingoperation.

Where air, or only one gas, is to constitute the atmosphere, inlet pipe25 and source 26 may be omitted. Also, a gas mixture containing gases indesired ratio of composition, may be admitted to inlet pipes 35 and 35'.Particular reference is made now to FIG. 3. A simplified configurationutilizing an arc heater may consist of a chamber 70 into which thedischarge from the nozzle 75 of the arc heater 71 is suitably directedto mix the gas volume in this chamber so as to obtain the desiredpressure, temperature uniformity, and gas composition in that part ofthe chamber where heating or heat treatment is to occur. Material to betreated is symbolized at 74. Temperature sensing can be as shown inFIG. 1. Excess gas removal from this chamber and pressure control can beaccomplished by a vent 72 located at any convenient location. Gas insidethe chamber follows the path indicated at 73.

Whereas we have shown and described three new and novel embodiments ofapparatus suitable for practicing the methods of our invention, it willbe understood that changes may be made and equivalents substitutedwithout departing from the spirit and scope of the invention.

We claim as our invention:

1. Arc heater loop apparatus suitable for heating of metals intempering, annealing, melting or reducing processes or processesrequiring heated gas flows comprising, in combination, an arc heaterhaving a gas input and a gas output, electrical circuit means connectedto the arc heater for bringing a potential thereto to form the arc andincluding means for regulating the power of the arc heater, furnacemeans including means forming a closed path, means including nozzlemeans for bringing the heated gas from the gas output of the arc heaterand injecting the heated gas into the closed path, the means forming aclosed path including chamber means adapted to have the metal to beheated placed therein, a temperature sensing device operativelyconnected to the chamber means for sensing the temperature therein, thetemperature sensing device being operably connected to the means forcontrolling the power to the arc heater, exhaust conduit means connectedto the furance means at a predetermined position for exhausting gas fromthe furnace means at a predetermined pressure and at a predeterminedrate of flow to maintain the pressure and the rate of gas flow in thefurnace means substantially constant, and means including compressormeans and heat exchanger means connected to the input of the arc heaterto supply gas thereto, the heat exchanger means being connected to theexhaust conduit means whereby the heat of gas exhausted from the furnacemeans preheats gas supplied as an input to the arc heater.

2. Arc heater loop apparatus for providing an atmosphere controlled asto pressure, temperature, gas content and rate of gas flow and suitablefor use in metal treating apparatus comprising, in combination, an archeater,

' circuit means including power regulating means connected to the archeater for providing an arc of variable intensity therein, meansincluding compressor means for supplying a compressed gas input to thearc heater, the

arc heater heating gas passing therethrough to a predeterminedtemperature in accordance with the power supplied thereto, furnace meansincluding means forming a closed path and having a throat portion andhaving a chamber therein, a nozzle disposed in the closed path formingmeans near the throat portion thereof and connected to the arc heater toreceive the heated gas therefrom, means for bringing an additional gasinto the furnace means obliquely to the gas from the nozzle means toprovide a well-mixed gas mixture in the furnace, the chamber beingadapted to have the metal to be heated placed therein, means for sensingtemperature variations in the gas in the chamber, the means for sensingtemperature variations being connected to the power regulating means andautomatically regulating the power to the arc heater in accordance withthe temperature of the gas in the chamber, a major portion of gasespassing through the chamber being recycled therethrough, and means forexhausting a predetermined minor portion of gas from the path formingmeans at a predetermined Cir pressure and at predetermined rate of flowto maintain the pressure and the rate of gas flow in the furnace meanssubstantially constant.

3. Are heater loop apparatus according to claim 2 including in additionheat exchanger means having the gas which is exhausted from the closedpath supplied thereto, the compressed gas passing through the heatexchanger prior to entry into the arc heater, precooler means connectedto the heat exchanger to receive the exhausted gas after passing throughthe heat exchanger, and dust separator means connected to the precoolermeans to receive the output therefrom, said compressor means beingconnected to the dust separator means to receive the output therefrom.

4. Arc heater loop apparatus comprising, in combination, an arc heaterhaving an energizing circuit, means for supplying compressed gas at apredetermined pres sure and rate of flow to the arc heater, furnacemeans including means forming a closed loop for the recycling of gasthrough the furnace means, means for supplying the heated gas output ofthe arc heater to the closed loop, the major portion of the gas in theclosed loop being recycled through the furnace means, means foradmitting an additional gas into the closed loop at a predetermined rateof flow to provide a gas mixture having substantially constantproportions, and means for removing a predetermined minor portion of gasfrom the closed loop at a predetermined pressure and rate of flow tomaintain the pressure and rate of gas flow in the furance meanssubstantially constant.

5. Arc heater loop apparatus comprising, in combination, an arc heaterhaving an energizing circuit, means for supplying compressed gas at apredetermined pressure and rate of flow to the arc heater, furnace meansincluding means forming a closed loop for the recycling of gas throughthe furnace means, means for supplying the heated gas output of the archeater to the closed loop, the major portion of the gas in the closedloop being recycled through the furnace means, means for removing apredetermined minor portion of gas from the closed loop at apredetermined pressure and rate of flow to maintain the pressure andrate of gas flow in the furance means substantially constant, and heatexchanger means connected in the means for removing gas from the closedloop, the heat exchanger means being connected to the means forsupplying compressed gas to the arc heater whereby the heat from gasremoved from the closed loop preheats the compressed gas prior to itsadmission to the arc heater.

6. Arc heater loop apparatus comprising, in combination, an arc heaterhaving an energizing circuit, means for supplying compressed gas at apredetermined pressure and rate of flow to the arc heater, furnace meansincluding means forming a closed loop for the recycling of gas throughthe furnace means, means for supplying the heated gas output of the archeater to the closed loop, a temperature sensing device disposed in thefurnace means, controllable means in the energizing circuit for the archeater for adjusting the power to the arc heater to thereby regulate thetemperature of the gas heated in the arc heater, means connecting thecontrollable means to the temperature sensing device whereby variationsin temperature in the furnace means automatically regulate the power tothe arc heater and there- -by regulate the temperature to which the gasis heated therein, the major portion of the gas in the closed loop beingrecycled through the furnace means, and means for removing apredetermined minor portion of gas from the closed loop at apredetermined pressure and rate of flow to maintain the pressure andrate of gas flow in the furnace means substantially constant.

7. Arc heater loop apparatus comprising, in combination, an arc heaterhaving an energizing circuit, means for supplying compressed gas at apredetermined pressure and rate of flow to the arc heater, furnace meansincluding means forming a closed loop for the recycling of gas throughthe furnace means, means for supplying the heated gas output of the archeater to the closed loop, the major portion of the gas in the closedloop being recycled through the furnace means, means for removing apredetermined minor portion of gas from the closed loop at apredetermined pressure and rate of flow to maintain the pressure andrate of gas flow in the furnace means substantially constant, means forprecooling and filtering that portion of gas removed from the closedloop, means for compressing the filtered gas, and means for applying thefiltered gas to the arc heater as a portion of the compressed gassupplied thereto.

8. Are heater loop apparatus comprising, in combination, an arc heaterhaving an energizing circuit, means for supplying compressed gas at apredetermined pressure and rate of flow to the arc heater, furnace meansincluding means forming a closed loop for the recycling of gas throughthe furnace means, means for supplying the heated gas output of the archeater to the closed loop, the major portion of the gas in the closedloop being recycled through the furnace means, means for admitting atleast a second gas to the closed loop at a predetermined rate of flow,the second gas being admitted at an angle oblique to the flow of gasfrom the arc heater to thereby provide a well-mixed gas mixture having apredetermined substantially constant ratio of composition, and means forremoving a predetermined minor portion of gas from the closed loop at apredetermined pressure and rate of flow to maintain the pressure andrate of gas flow in the furnace means substantially constant.

References Cited UNITED STATES PATENTS 1,896,910 2/1933 Merkt -1 -l.l58--1 2,252,319 8/1941 Holden 263'-14 2,504,320 4/ 1950 Gamble 263-432,639,910 5/1953 Cone et al. 263l5 3,010,009 11/1961 Ducati 2l91123,029,635 4/1962 Fetz 219-121 RICHARD M. WOOD, Primary Examiner.

C. L. ALBRITTON, Assistant Examiner.

